This invention relates to electrochromic rearview mirrors for motor vehicles and, more particularly, to improved electrochromic rearview mirrors incorporating third surface reflector/electrode in contact with at least one solution-phase electrochromic material.
Heretofore, various rearview mirrors for motor vehicles have been proposed which change from the full reflectance mode (day) to the partial reflectance mode(s) (night) for glare-protection purposes from light emanating from the headlights of vehicles approaching from the rear. Among such devices are those wherein the transmittance is varied by thermochromic, photochromic, or electro-optic (e.g., liquid crystal, dipolar suspension, electrophoretic, electrochromic, etc.) means and where the variable transmittance characteristic affects electromagnetic radiation that is at least partly in the visible spectrum (wavelengths from about 3800 xc3x85 to about 7800 xc3x85). Devices of reversibly variable transmittance to electromagnetic radiation have been proposed as the variable transmittance element in variable transmittance light fillers, variable reflectance mirrors, and display devices which employ such light filters or mirrors in conveying information. These variable transmittance light filters have included windows.
Devices of reversibly variable transmittance to electromagnetic radiation, wherein the transmittance is altered by electrochromic means, are described, for example, by Chang, xe2x80x9cElectrochromic and Electrochemichromic Materials and Phenomena,xe2x80x9d in Non-emissive Electrooptic Displays, A. Kmetz and K. von Willisen, eds. Plenum Press, New York, N.Y. 1976, pp. 155-196 (1976) and in various parts of Eletrochromism, P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCH Publishers, Inc., New York, N.Y. (1995). Numerous electrochromic devices are known in the art. See, e.g., Manos, U.S. Pat. No. 3,451,741; Bredfeldt et al., U.S. Pat. No. 4,090,358; Clecak et al., U.S. Pat. No. 4,139,276; Kissa et al., U.S. Pat. No. 3,453,038; Rogers, U.S. Pat. Nos. 3,652,149, 3,774,988 and 3,873,185; and Jones et al., U.S. Pat. Nos. 3,282,157, 3,282,158, 3,282,160 and 3,283,656.
In addition to these devices there are commercially available electrochromic devices and associated circuitry, such as those disclosed in U.S. Pat. No. 4,902,108, entitled xe2x80x9cSINGLE-COMPARTMENT, SELF-ERASING, SOLUTION-PHASE ELECTROCHROMIC DEVICES SOLUTIONS FOR USE THEREIN, AND USES THEREOFxe2x80x9d, issued Feb. 20, 1990, to Harlan J. Byker; Canadian Patent No. 1,300;945, entitled xe2x80x9cAUTOMATIC REARVIEW MIRROR SYSTEM FOR AUTOMOTIVE VEHICLES,xe2x80x9d issued May 19, 1992, to Jon H. Bechtel et al.; U.S. Pat. No. 5,128,799, entitled xe2x80x9cVARIABLE REFLECTANCE MOTOR VEHICLE MIRROR,xe2x80x9d issued Jul. 7, 1992, to Harlan J. Byker; U.S. Pat. No. 5,202,787, entitled xe2x80x9cELECTRO-OPTIC DEVICExe2x80x9d, issued Apr. 13, 1993, to Harlan J. Byker et al.; U.S. Pat. No. 5,204,778, entitled xe2x80x9cCONTROL SYSTEM FOR AUTOMATIC REARVIEW MIRRORS,xe2x80x9d issued Apr. 20, 1993, to Jon H. Bechtel; U.S. Pat. No. 5,278,693, entitled xe2x80x9cTINTED SOLUTION-PHASE ELECTROCHROMIC MIRRORS,xe2x80x9d issued Jan. 11, 1994, to David A. Theiste et al.; U.S. Pat. No. 5,280,380, entitled xe2x80x9cUV-STABILIZED COMPOSITIONS AND METHODS,xe2x80x9d issued Jan. 18, 1994, to Harlan J. Byker; U.S. Pat. No. 5,282,077, entitled xe2x80x9cVARIABLE REFLECTANCE MIRROR,xe2x80x9d issued Jan. 25, 1994, to Harlan J. Byker; U.S. Pat. No. 5,294,376, entitled xe2x80x9cBIPYRIDINIUM SALT SOLUTIONS,xe2x80x9d issued Mar. 15, 1994, to Harlan J. Byker; U.S. Pat. No. 5,336,448, entitled xe2x80x9cELECTROCHROMIC DEVICES WITH BIPYRIDINIUM SALT SOLUTIONS,xe2x80x9d issued Aug. 9, 1994, to Harlan J. Byker; U.S. Pat. No. 5,434,407, entitled xe2x80x9cAUTOMATIC REARVIEW MIRROR INCORPORATING LIGHT PIPE,xe2x80x9d issued Jan. 18, 1995, to Frederick T. Bauer et al.; U.S. Pat. No. 5,448,397, entitled xe2x80x9cOUTSIDE AUTOMATIC REARVIEW MIRROR FOR AUTOMOTIVE VEHICLES,xe2x80x9d issued Sep. 5, 1995, to William L. Tonar; and U.S. Pat. No. 5,451,822, entitled xe2x80x9cELECTRONIC CONTROL SYSTEM,xe2x80x9d issued Sep. 19, 1995, to Jon H. Bechtel et al. Each of these patents is commonly assigned with the present invention and the disclosures of each, including the references contained therein, are hereby incorporated herein in their entirety by reference. Such electrochromic devices may be utilized in a fully integrated inside/outside rearview mirror system or as separate inside or outside rearview mirror systems.
FIG. 1 shows a typical electrochromic mirror device 10, having front and rear planar elements 12 and 16, respectively. A transparent conductive coating 14 is placed on the rear face of the front element 12, and another transparent conductive coating 18 is placed on the front face of rear element 16. A reflector (20a, 20b and 20c), typically comprising a silver metal layer 20a covered by a protective copper metal layer 20b, and one or more layers of protective paint 20c, is disposed on the rear face of the rear element 16. For clarity of description of such a structure, the front surface of the front glass element is sometimes referred to as the first surface, and the inside surface of the front glass element is sometimes referred to as the second surface. The inside surface of the rear glass element is sometimes referred to as the third surface, and the back surface of the rear glass element is sometimes referred to as the fourth surface. The front and rear elements are held in a parallel and spaced-apart relationship by seal 22, thereby creating a chamber 26. The electrochromic medium 24 is contained in space 26. The electrochromic medium 24 is in direct contact with transparent electrode layers 14 and 18, through which passes electromagnetic radiation whose intensity is reversibly modulated in the device by a variable voltage or potential applied to electrode layers 14 and 18 through clip contacts and an electronic circuit (not shown).
The electrochromic medium 24 placed in space 26 may include surface-confined, electrodeposition type or solution-phase type electrochromic materials and combinations thereof. In an all solution-phase medium, the electrochemical properties of the solvent, optional inert electrolyte, anodic materials, cathodic materials, and any other components that might be present in the solution are preferably such that no significant electrochemical or other changes occur at a potential difference which oxidizes anodic material and reduces the cathodic material other than the electrochemical oxidation of the anodic material, electrochemical reduction of the cathodic material and the self-erasing reaction between the oxidized form of the anodic material and the reduced form of the cathodic material.
In most cases, when there is no electrical potential difference between transparent conductors 14 and 18, the electrochromic medium 24 in space 26 is essentially colorless or nearly colorless, and incoming light (IO) enters through front element 12, passes through transparent coating 14, electrochromic containing chamber 26, transparent coating 18, rear element 16, and reflects off layer 20a and travels back through the device and out front element 12. Typically, the magnitude of the reflected image (IR) with no electrical potential difference is about 45 percent to about 85 percent of the incident light intensity (IO). The exact value depends on many variables outlined below, such as, for example, the residual reflection (Ixe2x80x2R) from the front face of the front element, as well as secondary reflections from the interfaces between: the front element 12 and the front transparent electrode 14; the front transparent electrode 14 and the electrochromic medium 24; the electrochromic medium 24 and the second transparent electrode 18; and the second transparent electrode 18 and the rear element 16. These reflections are well known in the art and are due to the difference in refractive indices between one material and another as the light crosses the interface between the two. If the front element and the back element are not parallel, then the residual reflectance (Ixe2x80x2R) or other secondary reflections will not superimpose with the reflected image (IR) from mirror surface 20a, and a double image will appear (where an observer would see what appears to be double (or triple) the number of objects actually present in the reflected image).
There are minimum requirements for the magnitude of the reflected image depending on whether the electrochromic mirrors are placed on the inside or the outside of the vehicle. For example, according to current requirements from most automobile manufacturers, inside mirrors must have a high-end reflectivity of at least 70 percent and outside mirrors must have a high-end reflectivity of at least 50 percent.
Electrode layers 14 and 18 are connected to electronic circuitry which is effective to electrically energize the electrochromic medium, such that when a potential is applied across the transparent conductors 14 and 18, electrochromic medium in space 26 darkens such that incident light (IO) is attenuated as the light passes toward the reflector 20a and as it passes back through after being reflected. By adjusting the potential difference between the transparent electrodes, such a device can function as a xe2x80x9cgray-scalexe2x80x9d device, with continuously variable transmittance over a wide range. For solution-phase electrochromic systems, when the potential between the electrodes is removed or returned to zero, the device spontaneously returns to the same, zero-potential, equilibrium color and transmittance as the device had before the potential was applied. Other electrochromic materials are available for making electrochromic devices. For example, the electrochromic medium may include electrochromic materials that are solid metal oxides, redox active polymers and hybrid combinations of solution-phase and solid metal oxides or redox active polymers; however, the above-described solution-phase design is typical of most of the electrochromic devices presently in use.
Even before a fourth surface reflector electrochromic mirror was commercially available, various groups researching electrochromic devices had discussed moving the reflector from the fourth surface to the third surface. Such a design has advantages in that it should, theoretically, be easier to manufacture because there are fewer layers to build into a device, i.e., the third surface transparent electrode is not necessary when there is a third surface reflector/electrode. Although this concept was described as early as 1966, no group had commercial success because of the exacting criteria demanded from a workable auto-dimming mirror incorporating a third surface reflector. U.S. Pat. No. 3,280,701, entitled xe2x80x9cOPTICALLY VARIABLE ONE-WAY MIRROR,xe2x80x9d issued Oct. 25, 1966, to J. F. Donnelly et al. has one of the earliest discussions of a third surface reflector for a system using a pH-induced color change to attenuate light.
U.S. Pat. No. 5,066,112, entitled xe2x80x9cPERIMETER COATED, ELECTRO-OPTIC MIRROR,xe2x80x9d issued Nov. 19, 1991, to N. R. Lynam et al. teaches an electro-optic mirror with a conductive coating applied to the perimeter of the front and rear glass elements for concealing the seal. Although a third surface reflector is discussed therein, the materials listed as being useful as a third surface reflector suffer from one or more of the following deficiencies: not having sufficient reflectivity for use as an inside mirror, or not being stable when in contact with a solution-phase electrochromic medium containing at least one solution-phase electrochromic material.
Others have broached the topic of a reflector/electrode disposed in the middle of all solid state-type devices. For example, U.S. Pat. Nos. 4,762,401, 4,973,141, and 5,069,535 to Baucke et al. teach an electrochromic mirror having the following structure: a glass element; a transparent (ITO) electrode; a tungsten oxide electrochromic layer; a solid ion-conducting layer; a single layer hydrogen ion-permeable reflector; a solid ion conducting layer; a hydrogen ion storage layer; a catalytic layer; a rear metallic layer; and a back element (representing the conventional third and fourth surface). The reflector is not deposited on the third surface and is not directly in contact with electrochromic materials, certainly not at least one solution-phase electrochromic material and associated medium.
Consequently, it is desirable to provide an improved high reflectivity electrochromic rearview mirror having a third surface reflector/electrode in contact with a solution-phase electrochromic medium containing at least one electrochromic material.
Aspects of the present invention, which will become apparent from the specification as a whole, including the drawings, are accomplished in accordance with the present invention by incorporating a reflector/electrode on the inside (third) surface of a dimming portion of the rearview mirror. This reflector/electrode forms an integral electrode in contact with at least one solution-phase electrochromic material, and may be a single layer of a highly reflective silver alloy or may comprise a series of coatings where the outer coating is a highly reflective silver alloy. When a series of coatings is used for the reflector/electrode, there should be a base coating which bonds to the glass surface and resists any adverse interaction, e.g., corrosive action, with any constituents of the electrochromic medium, an optional intermediate layer (or layers) which bonds well to the base coating and resists any adverse interaction with the electrochromic medium, and at least one highly reflective silver alloy which directly contacts the electrochromic medium and which is chosen primarily for its adequate bond to the peripheral seal, its high reflectance, good shelf life, stable behavior as an electrode, resistance to adverse interaction with the electrochromic medium, resistance to atmospheric corrosion, resistance to electrical contact corrosion, and the ability to adhere to the base or intermediate layer(s), if present. If a single layer of highly reflective silver alloy is utilized, it must also meet these operational criteria.
In another embodiment of the present invention, when a very thin over-coating is placed over the highly reflective layer, then the highly reflective layer may be silver metal or a silver alloy.
In yet another embodiment of the present invention, the third surface reflector/electrode includes at least one base layer that is disposed over the entire third surface of the electrochromic mirror. A highly reflective layer is disposed over the central portion of the base layer(s) and not over the perimeter edge portion where the seal will be placed. Optionally, one or more intermediate layers may be disposed between the base and reflective layers, and may be placed over the entire third surface, or may be placed over the central portion or both (if there is more than one intermediate layer).
The third surface reflector of the present invention may additionally provide for significant improvement of the electrical interconnection techniques used to impart a voltage or drive potential to the transparent conductor on the second surface of the electrochromic mirror. This is accomplished both by providing improved contact stability between the contacts, such as clips, and the reflector layer and by providing unique and advantageous buss bar configurations.